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Host (network)

Host (network)

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A network host is a computer
A computer is a programmable machine designed to sequentially and automatically carry out a sequence of arithmetic or logical operations. The particular sequence of operations can be changed readily, allowing the computer to solve more than one kind of problem...

 connected to a computer network
Computer network
A computer network, often simply referred to as a network, is a collection of hardware components and computers interconnected by communication channels that allow sharing of resources and information....

. A network host may offer information resources, services, and applications to users or other nodes
Node (networking)
In communication networks, a node is a connection point, either a redistribution point or a communication endpoint . The definition of a node depends on the network and protocol layer referred to...

 on the network. A network host is a network node that is assigned a network layer
Network layer
The network layer is layer 3 of the seven-layer OSI model of computer networking.The network layer is responsible for packet forwarding including routing through intermediate routers, whereas the data link layer is responsible for media access control, flow control and error checking.The network...

 host address
Host address
The host address, or the host ID portion of an IP address, is the portion of the address used to identify hosts on the network...


Computers participating in networks that use the Internet Protocol Suite
Internet protocol suite
The Internet protocol suite is the set of communications protocols used for the Internet and other similar networks. It is commonly known as TCP/IP from its most important protocols: Transmission Control Protocol and Internet Protocol , which were the first networking protocols defined in this...

 may also be called IP hosts. Specifically, computers participating in the Internet
The Internet is a global system of interconnected computer networks that use the standard Internet protocol suite to serve billions of users worldwide...

 are called Internet hosts, sometimes Internet nodes. Internet hosts and other IP hosts have one or more IP address
IP address
An Internet Protocol address is a numerical label assigned to each device participating in a computer network that uses the Internet Protocol for communication. An IP address serves two principal functions: host or network interface identification and location addressing...

es assigned to their network interfaces. The addresses are configured either manually by an administrator, automatically at start-up by means of the Dynamic Host Configuration Protocol
Dynamic Host Configuration Protocol
The Dynamic Host Configuration Protocol is a network configuration protocol for hosts on Internet Protocol networks. Computers that are connected to IP networks must be configured before they can communicate with other hosts. The most essential information needed is an IP address, and a default...

 (DHCP), or by stateless address autoconfiguration methods.

Every network host is a physical network node (i.e. a network device), but not every physical network node is a host. Network devices such as modem
A modem is a device that modulates an analog carrier signal to encode digital information, and also demodulates such a carrier signal to decode the transmitted information. The goal is to produce a signal that can be transmitted easily and decoded to reproduce the original digital data...

s, hubs
Ethernet hub
An Ethernet hub, active hub, network hub, repeater hub or hub is a device for connecting multiple Ethernet devices together and making them act as a single network segment. A hub works at the physical layer of the OSI model. The device is a form of multiport repeater...

 and network switch
Network switch
A network switch or switching hub is a computer networking device that connects network segments.The term commonly refers to a multi-port network bridge that processes and routes data at the data link layer of the OSI model...

es are not assigned host address
Host address
The host address, or the host ID portion of an IP address, is the portion of the address used to identify hosts on the network...

es (except sometimes for administrative purposes), and are consequently not considered as network hosts. Devices such as network printers and hardware routers have IP addresses, but since they are not general-purpose computers, they are sometimes not considered as hosts.

Network hosts that participate in applications that use the client-server model of computing, are classified as server
Server (computing)
In the context of client-server architecture, a server is a computer program running to serve the requests of other programs, the "clients". Thus, the "server" performs some computational task on behalf of "clients"...

 or client
Client (computing)
A client is an application or system that accesses a service made available by a server. The server is often on another computer system, in which case the client accesses the service by way of a network....

 systems. Network hosts may also function as nodes in peer-to-peer
Peer-to-peer computing or networking is a distributed application architecture that partitions tasks or workloads among peers. Peers are equally privileged, equipotent participants in the application...

 applications, in which all nodes share and consume resources in an equipotent manner.

Server and Host

Host Server
Always a physical node Can be a physical node or a software program
Can run both server and client programs Installed on a host
Provides specific services Provides specific services
Serves multiple users and devices Serves only clients

Origin of the concept

In operating systems, the term terminal host traditionally denotes a multi-user
Multi-user is a term that defines an operating system or application software that allows concurrent access by multiple users of a computer. Time-sharing systems are multi-user systems. Most batch processing systems for mainframe computers may also be considered "multi-user", to avoid leaving the...

 computer or software providing services to computer terminal
Computer terminal
A computer terminal is an electronic or electromechanical hardware device that is used for entering data into, and displaying data from, a computer or a computing system...

s, or a computer that provides services to smaller or less capable devices, such as a main frame computers serving teletype terminals or video terminals. Other examples are a telnet
Telnet is a network protocol used on the Internet or local area networks to provide a bidirectional interactive text-oriented communications facility using a virtual terminal connection...

 host (a telnet server) and an xhost (X Window client).

The term "Internet host" or just "host" is used in a number of Request for Comments
Request for Comments
In computer network engineering, a Request for Comments is a memorandum published by the Internet Engineering Task Force describing methods, behaviors, research, or innovations applicable to the working of the Internet and Internet-connected systems.Through the Internet Society, engineers and...

 (RFC) documents that define the Internet and its predecessor, the ARPANET
The Advanced Research Projects Agency Network , was the world's first operational packet switching network and the core network of a set that came to compose the global Internet...

. While the ARPANET was developed, computers connected to the network were typically main frame computer systems that could be accessed from terminals connected via serial port
Serial port
In computing, a serial port is a serial communication physical interface through which information transfers in or out one bit at a time...

s. Since these dumb terminals did not host software or perform computations themselves, they were not considered hosts. The terminals were connected to the terminal hosts through serial interfaces and perhaps circuit switched networks, but not connected to any IP based network, and were not assigned IP addresses. Today's IP hosts may, however, lack ability to serve as terminal hosts.

RFC 871 defines a host, as a general-purpose computer system connected to a communications network for "... the purpose of achieving resource sharing amongst the participating operating systems,...".